Imperial Japanese Navy "Destroyer Warabi" Search Project II - Discovery After 93 Years
The destroyer Warabi, which sank due to an accident during military exercises off the coast of Mihonoseki in Shimane Prefecture, remained shrouded in mystery for a long time despite being a major incident that claimed many lives. However, in September 2020, the World Scan Project (W.S.P.), underwater archaeologist Kotaro Yamafune, and the Kyushu University Research Center for Coastal Seafloor (Professor Hironobu Suga) conducted a joint investigation, and the Warabi was finally revealed after 93 years.
*Please refer to the following article for more information about the "Mihonoseki Incident," where the destroyer Warabi sank.
The Path to the Discovery of the Warabi
The coordinates for the survey were determined based on data created by the multi-beam sonar at the Kyushu University Research Center for Coastal Seafloor (which precisely measured the seabed topography), and two on-site surveys were conducted in September 2020 and July 2021.
First Survey: Discovery of the Bow
In the first survey, the underwater 3D scanning robot "Murakumo" successfully captured clear images of the sunken object at a depth of approximately 96 meters. The footage revealed the bow section of the Warabi, which had been split in two due to the impact of an explosion, making it an exciting discovery for the entire team.
Second Survey: Discovery of the Stern, Unveiling the Full Picture
Following the discovery in the first survey, the team decided to use Murakumo again to search for the remaining parts of the Warabi. The second survey was conducted approximately 10 kilometers north-northwest of where the bow was found, at a deeper depth of approximately 180 meters.
Exploring at a depth of 180 meters was challenging, but Murakumo demonstrated its powerful capabilities and delivered remarkable results.
The images transmitted from underwater revealed the stern of the Warabi, bearing the severe marks of its sinking. This moment brought a piece of history back to life before our eyes. The discovery, which shed light on the long-unsolved mystery of the destroyer Warabi, was widely covered in newspapers and on television, becoming significant news for the members of the "Mihonoseki Offshore Incident Memorial Association" who had eagerly awaited this discovery.
Underwater 3D Scanning Robot "Murakumo"
The discovery of the Warabi was made possible by the advanced underwater 3D scanning robot "Murakumo," developed by the World Scan Project (W.S.P.).
Murakumo is capable of precisely scanning the complex topography of the seabed and creating 3D models using photogrammetry techniques. Its accuracy reaches millimeter levels, allowing for detailed data collection that was previously impossible with conventional technologies, from seabed topography to environmental information.
Additionally, Murakumo excels at wide-area scanning, ranging from several kilometers to tens of kilometers, making it ideal for not only shipwreck investigations but also submarine cable inspections and pre-construction assessments for offshore wind farms across various industries.
In the search for the Warabi, Murakumo succeeded in visualizing difficult-to-see parts such as cylindrical structures believed to be triple gun turrets and portholes, even under the challenging conditions of murky waters at depths exceeding 100 meters.
Another feature of Murakumo is its low operational cost. Typically, underwater drone surveys require vessels equipped with large cranes, costing several million yen per day. However, Murakumo can significantly reduce these costs.
Thus, the method using Murakumo, capable of performing imaging even under adverse underwater conditions while keeping costs low, represents a significant advance in underwater exploration.
An Opportunity to Focus on Valuable Underwater Relics
The 3D model of the Warabi revealed the extent of the hull damage. In addition to the significant passage of time since its sinking, the hull's deterioration was further exacerbated by bottom trawling vessels passing through the area.
The ship's features, such as navigation lights and turrets, could not be identified, and the hull was entangled in numerous nets. It is believed that bottom trawling in the vicinity has significantly affected the condition of the vessel. In addition, fishing activity in the area has declined in recent decades due to damage to fishing vessels and nets caught on underwater structures such as the Warabi.
Underwater archaeologist Kotaro Yamafune reflected on the findings, saying, "These kinds of underwater relics exist worldwide, providing an excellent case study to understand the impact of underwater sites on maritime activities and vice versa."
Proving History and Bridging Generations through 3D Modeling
The goal of this project was to discover and accurately capture the Warabi, which lies at the bottom of the deep sea. Murakumo undertook long underwater operations in challenging conditions that were difficult for humans to handle, leading to the project's success. Moreover, the millimeter-precision 3D model of the Warabi, brought back to life, holds historical value and was used in local reporting sessions by the Mihonoseki Offshore Incident Memorial Association, providing invaluable evidence to substantiate the oral traditions passed down over generations.
As underwater archaeologist Kotaro Yamafune states, "Just like the Hiroshima Peace Memorial (Genbaku Dome), it's crucial to preserve the actual physical evidence as witnesses of history. Creating 3D models that anyone can access serves not only educational, research, and monitoring purposes but also plays a significant role in the preservation of history."
The seabed still holds numerous valuable artifacts and information that are a part of history. World Scan Project (W.S.P.) aims to discover and protect such heritage, intending to pass on the historical value of humanity's legacy to future generations.
Going forward, the World Scan Project (W.S.P.) will continue to bridge the past and future through the integration of history and technology, constantly challenging the mysteries of the unknown ocean world.
Watch videos to learn more about the Destroyer Warabi Search Project.
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